Borehole drilling apparatus for preventing lost circulation



Aug. 26, 1958 J. l. HALL BOREHOLE DRILLING APPARATUS FOR PREVENTING LosT CIRCULATION Filed sept. 2. 1954 Nr w United States Patent G BOREHOLE DRILLING APPARATUS FOR PREVENTING LOST CIRCULATION John I. Hall, Lourenco Marques, Mozambique, Portuguese East Africa, assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Application September 2, 1954, Serial No. 453,899

4 Claims. (Cl. Z55-24) This invention relates to improvements in drilling apparatus, the invention having more particular reference to the rotary drilling of boreholes of moderate depth in cavernous and fissured formations wherein excessive loss of drilling fluid is ordinarily encountered.

vIt is the practice in rotary drill-ing to insert casing after =a hole of particular size has reached desired depth, following which drilling proceeds with a sm-aller bit run through the casing then in place. In shot holes, such as seismic prospecting shot holes which `are of moderate depth, casing may not be needed, or if it is, it is inserted lafter the hole has been completed, lIn either case large Iareas of the Iformation are exposed =as the -bit progresses downwardly. If the hole penetra-tes Aa cavernous formation Ilost circulation of drilling fluid may, and frequently does result since in conventional practice the fluid` is pumped down the drill column and returns to the surface in contact with the exposed formation.

In accordance with this invention, the drilling duid is isolated from the wall of the hole except in the immediate Vicinity of the bit so that loss of fluid into the formation is minimized. To this end the drill pipe comprising the column is of multi-duct construction having separate water ways for fluid pumped into the hole and forits return to the lsurface 'with the chips removed in cutting. A part of the pumped iluid is jetted into the bottom of the hole to clean the bit land stir up chips by turbulence and agitation, while its greater part is diver-ted to upwardly-directed nozzles in the drill pipe above the bit. These nozzles are in alignment with and directed toward venturi tubes communicating with the return ducts in the` drillpipe, whereby suction created by the increased velocity of the fluid at the venturi orifices assists in drawing the cuttings by jetting action into the return flow and their consequent removal from the hole with the circulated iluid.

-It is an object `of my invention to minimize lost circulation by isolating the ow of drilling fluid both into and out of the drilled hole so that it comes only briefly into contact with the exposed formation in the immediate vicinity of the bi-t.

Another object of the invention is to produce a cleanlydrilled hole from which cuttings lare ushed as they are formed, by creating a turbulent flow yof drilling iluid around the bit `and in a region of suction which is induced by jetting 1a part of the fluid through venturi tubes in return ducts Within the drill pipe.

A Ifurther object of the invention is to provide a drill column comprising concentric, spaced pipes which are assembled :as Ia u nit to afford rigidity to the column and thus to facilitate the drilling of a straight hole.

Other objects and advantages of this invention will be apparent from the following description and drawings in which:

Figure l is a longitudinal sectional View of the drill column;

Figure 2 is a cross-sectional view taken Ialong line 2,849,214 Patented Aug. 26, 1958 'II-4H of Figure 1, las viewed in the direction of the arrows;

Figure 3 is Ia cross-sectional view taken along line -I'IIAIH of Figure 1 as viewed in the direction of the arrows; and

Figure 4 is a cross-sectional view taken along line lIV--IV of Figure 1 as viewed in the direction of the arrows.

Referring more particularly to the drawings, the drill column comprises outer and inner pipes 10 and 11 which are secured together in concentric, spaced relation. 'Ihe outer pipe may conveniently comprise sections of 317/2 inch O. D. casing While the inner pipe may comprise A. lP. I. standard type B drill pipe which is 12S/32 inch O. D. yBridging pieces l2 better shown in Figure 2, three or more in number, `are arranged as shown in Figure 2 to space the pipes 10 and 11, and where the pipes are of the above-exemplified sizes, such bridging pieces may be made of parallel key stock. The bridging pieces 12 are welded to the inner pipe before its assembly within the outer pipe and `are thereafter welded to the outer pipe through slots 13 previously milled in the wall of the pipe l@ for this purpose as shown in Figure 3, after the threads of both male 'and female ends of the pipe sections have been matched by their starting threads. For the latter purpose previously-made male and female jigs are applied to each end of the pipes 1lb and 11 in order to properly match the threads so that when additional lengths of the double-pipe column are screwed together the threaded joints of both the inner and outer pipes make up tightly in unison. The assembled sections of pipes 10 and 11 are thus available to extend the drill column as the drill .penetrates the ground.

At the upper end of Ithe drill column there is screwed onto the column a standard square kelly (not shown) which is driven by a rotary table in conventional manner, and by means of which the drill column and drill are rotated. The kelly also has welded inside it an inner pipe so ias to match the upper end of the drill column. By the use of a double swivel at the top of the composite kelly, drilling fluid m-ay be pumped down the inner pipe 11 to the drill and the drilling fluid returns to the surface through the annular space 43 between the pipes 10 and 11.

Screwed to the lower end of the composite drill pipe there is a special outer pipe sub 14 having female threads at each end as -shown in Figure 1. Screwed to the lower end of ysub 14 is a venturi tube holder 15, the latter being drilled with two pairs of holes 16 and 17. Holes 16 have at their lower end a shoulder 18 which serves to retain venturi tubes 19. The tubes 19 fit into the holes 16 and have at their lower end a reduced diameter to form a shoulder which rests on shoulder 1S. The tubes are provided with O-ring seals 20 where they are supported on the shoulders 1S. The other pair of holes 17 are water-course holes and are located on a line at right angles to the transverse line of holes 16, and may be located under the holes 21 shown in Figure 3 to be described later.

The venturi tubes 19 are each provided at their lower end with a venturi orifice or throat 22 which may be pressed into the tube or otherwise securely fastened therein. The venturi tubes themselves must be long enough to impart an upward velocity to the returning drilling fluid and a length of about 3 feet has been found satisfactory. The upper end of each venturi tube abuts against a shouldered opening in transverse plate 23 whose top surface is seen in Figure 3. O-ring seals 24 (Figure 1) may be used to seal the end of tubes 19 against plate 23. The plate 23 may freely rotate inside of outer sub 14 and abuts on its upper s urface against three or more stops 25 which are welded to the inside surface of sub 14. The

lower edges of stops lie in a transverse plane properly distanced from the lower end of sub 14 so that in assembly the tubes 19 are placed in their holder 15 and the plate 23 placed on top of the tubes 19, after which the holder 15 and sub 14 are screwed together and the plate comes tightly up against the stops 25, whereby the venturi tubes are securely held in position. yO-ring 44 seals plate 23 against sub 14.

Referring now to that portion of Figure 1 extending between the sections II-II and III-III, the lower end of inner pipe 11 screws into a piece of pipe 26 which at its lower end is welded onto the top of plate 23. The lower end of pipe 26 also has cut out two diametrically-opposed sections 27 which are closed by pieces -of suitably-curved metal plates 28 which are welded to the pipe26 and to the plate 23 to cover the `sections 27. The recesses thus formed in the regions 27 permit the upwardflowing fluid from the venturi tubes 19 to clear the lower end of pipe 26. Two holes 21 are drilled through the plate 23 inside the region defined by the pipe 26 and the plates 28, the holes 21 thus carrying downward-owing fluid into the space 29, whence the iluid enters the water-course holes 17 previously mentioned.

The lower end of the venturi holder 15 is reduced in diameter to a diameter substantially smaller than the root diameter of threads 41, the smaller diameter being indicated by 30 (as best shown in Figure 4) and this is further reduced and threaded at 31 for the drill-bit sub 32 as shown in Figure l. The venturi holder 15 thus functions as the bit holder and serves to transmit torque from the drill pipe to the drill bit. Two diametrically opposite recesses 33 are milled in the region of reduced diameter 30 as best shown in Figure 4. These recesses expose the holes 16, and the lower end of the venturi tubes 19 with the venturi throats 22 protrude into the recesses. 'I

Directly below and in line with the holes 16 there are drilled and tapped the holes 34.v Upwardly-directed nozzles 35 are screwed into these holes prior to assembly of the venturi tubes 19, the length of the nozzles 35 being less than the length of the recesses 33. The nozzles may be provided with hexagonal wrench flats as shown so that they may be tightened in the holes 34. The lower end of the venturi holder is drilled out as lshown at 36, the Ibore 36 being suliiciently large in diameter so that it communicates with the water-course holes 17. Transverse holes 37 are then drilled to intersect both the holes 34 and the bore 36 and thereby provide communication from the bore 36 to the nozzles 35. The transverse holes 37 may be drilled from outside and the outer end afterward closed with a plug (not shown) welded in place in well-known manner.

The bit sub 32 carries at its lower end a conventional drill bit 38 having passageways 39 which carry drilling uid from the bore 36 directly to the bit where it may be discharged as a jet into the bottom of the borehole as is conventional in the art. Any known type of drill bit may be used, the drill 'bit per se not being my invention. While aI cone bit is shown in Figure l my invention may use a {ish-tail =bit or other known type.

The venturi holder 15 is threaded as at 41 and a shield 42 screwed thereon. The shield 42 extends downward around the recesses 33 and terminates a short distance above the upper part o f the drill bit 38. The inside diameter of the shield 42 is substantially larger than the diameter 30, thus providing an annular space 40 through which the upward-flowing drilling iluid returning from the bit 38 may find ready access to the lower end of the venturi tubes. The shield 42 should be the same outside diameter or larger than the outer drill pipe 10 and should be smaller than the outside diameter of the drill bit 38.

In drilling with my invention, the assembly of Figure 1 is rotated and drilling uid is concurrently pumped down the inner pipe 11. The uid is carried by pipe 26 and holes 21 into the space 29, whence it ows through holes 17 into the bore 36 and some of it flows directly to the borehole through passageways 39. In its downward flow, a substantial part of the drilling' lluid is diverted into lateral passages 37 which branch from the bore 36, and these branch passages terminate in the upwardly-directed nozzles 35 which are in alignment with the venturi throats 22 in tubes 19. The shield 42 which forms a downward extension of the outer drill pipe 10 surrounds the jets so that iluid circulated through the drill bit comes into only brief contact with the exposed formation `being drilled. Drilling fluid filling the bottom of the borehole and the space within the shield 42 is in turbulent flow thus serving to agitate and suspend the drillA cuttings. The upwardlydirected jets emerging from the nozzles 35 are accelerated in their flow through the venturi throats 22 and create a suction which draws the fluid from the bottom of the borehole upwardly throughthe venturi tubes 19 and discharges it into the annular return flow passage 43 between the inner and outer drill pipes. At the surface the cuttings may be separatedl from the drilling fluid and the latter recirculated as is conventional in the art.

By the use of my invention the formation being drilled is exposed to drilling lluid for only a short distance above the bit. The region of the borehole above the shield 42 is protected from the drilling fluid so that there is substantially no interchange of fluid between previouslydrilled formations higher up in the borehole and the circulating-uid system of the drill.

The pressure of the fluid in the borehole surrounding'.`

the bit may be adjusted somewhat by the size of orifices in the nozzles 35 and the venturi throats 22', as compared with the passageways 39 in the bit. Thus the suction created by the venturi tubes may be made great enough so that a pressure slightly less than hydrostatic prevails" in the borehole around the bit, or slightly greater than hydrostatic. I prefer to so adjust the nozzles and'flow passages that the pressure in the region around the bit is approximately equal to the hydrostatic pressure. In this manner there is little or no tendency for uid to enter a formation being drilled andv which might cause lost circulation, and also little or no tendency for formation water to enter the borehole at the drill. Alternatively, I have found it useful in certain areas t'o so adjust the size of the nozzles as to operate with pressure somewhat less than hydrostatic in the borehole at the bit, since by so doing there is a tendency to withdraw a slight amount of'y water from formations being drilled so as to make up for drilling iluid normally lost in the pits at the surface or left behind when the drill is moved from one location to a new one. Either of these pressure conditions avoid loss of circulating fluid, which is a very important desideratum in many instances, e. g. when drilling seismo- -graph shot holes in arid regions.

It is to be understood that my invention is not limited in its application to the drilling of shot holes 'or other boreholes of shallow to moderate depth. It will be apparent that the unitary assemblage ofrconcentric pipe contributes greatly to the rigidity of the drill column and affords separate ducts which isolate the Vcirculated fluid from the formation penetrated b y the hole, so that as a consequence straight and clean hole may be drilled with minimum lost circulation. My invention may be operated with aqueous drilling tluids or with other conventional liquid-type drilling fluids such aswell known oil or emulsion muds, and it may be operated with air as the'drillng fluid. Furthermore, the construction of my drill is such that in many cases standardized partsrnay be used in the assembly.

In the appended claims the element 15 is termed bit holder inasmuch as it functions to transmit drilling torque and weight to the drill bit as well as forming a convenient mount for the nozzles and venturi tubes.

What I claim as my invention is:

l. Rotary drilling apparatus wherein a drillv pipe carries at its lower end a bit holder with drill bit attachedy thereto comprising a drill pipe providing a, fluid-supply passage and an associated fluid-return passage, a bit holder rigidly connected to said drill pipe, a fluid-ow channel from saidfluid-supply passage through said bit holder adapted to supply uid to the drill bit, an upwardly-directed nozzle in said bit holder, a fluid-flow channel from said duid-supply channel to said nozzle, a venturi tube in said bit holder spaced above said nozzle and axially aligned with said nozzle, a fluid-How channel alfording iluid communication from the borehole immediately above the drill bit to the lower end of said venturi tube, and a uid-ow channel from the upper end of said venturi tube to said uid-return passage.

2. Rotary drilling apparatus wherein a drill pipe carries at its lower end a bit holder with drill bit attached thereto comprising a drill pipe having a uidsupply duct and an associated fluid-return duct, a bit holder rigidly connected to said drill pipe, a uid-ow channel from said uid-supply duct through said bit holder adapted to supply uid to the drill bit, an upwardly-directed nozzle in said bit holder, a uid-flow channel from said uid-supply duct to said nozzle, a venturi tube in said bit holder spaced above said nozzle and axially aligned with said nozzle, a fluid-flow channel aiording fluid communication from the borehole immediately above the drill bit to the lower end of said Venturi tube, and a duid-flow channel from the upper end of said venturi tube to said uid-return duct.

3. Rotary drilling apparatus wherein a drill pipe carries at its lower end a bit holder with drill bit attached thereto comprising a drill pipe having a Huid-supply duct and a concentric fluid-return duct rigidly connected thereto, a bit holder rigidly connected to the drill pipe and having an outside diameter substantially the same as the outside diameter of the drill bit to be used, a tluidflow channel from said fluid-supply duct through said bit holder adapted to supply uid to the drill bit, an upwardly-directed nozzle in said bit holder, a uid-ow channel from said fluid-supply duct to said nozzle, a venturi tube in said bit holder spaced above said nozzle and axially aligned with said nozzle, a uid-ow channel affording uid communication from the borehole region between the drill bit and the bit holder to the lower end of said venturi tube, and a fluid-flow channel from the upper end of said venturi tube to said uid-return duct.

4. Rotary drilling apparatus wherein a drill pipe carries at its lower end a bit holder with drill bit attached thereto comprising a drill pipe having a fluid-supply duct and an associated uid-return duct, a bit holder rigidly connected to the Adrill pipe, a fluid-flow channel leading from said fluid-supply duct through said bit holder adapted to supply fluid to the drill bit, an upwardly-directed nozzle in said bit holder, a uid-ilow channel from said fluid-supply duct to said nozzle, a venturi tube in said bit holder spaced above said nozzle and axially aligned with said nozzle, an annular shield connected to the bit holder and extending downward from the bit holder to the proximity of the drill bit, a uid-ow channel affording Huid communication from the borehole region between the drill bit and the lower end of said shield to the lower end of said venturi tube, and a uidow channel from the upper end of said venturi tube to said fluid-return duct.

References Cited in the file of this patent UNITED STATES PATENTS 

